The present invention relates generally to scanners, and more specifically the invention pertains to a PLZT based electro-optic phased array optical scanner. This technology is related to the U.S. patent application, Ser. No. 08/372,256 filed on 13 Jan. 1995 entitled "HIGH EFFECIENCY POLYCRYSTALLINE PLZT CERAMIC ELECTRO-OPTIC PHASE GRATING WITH ITO ELECTRODES" by Pierre J. Talbot the disclosure of which is incorporated herein by reference.
Optical scanning is the geometric reorientation of an optical beam's pathway. A device that efficiently and conveniently implemented optical scanning would have wide application. In particular, integrated optical scanning devices would offer the opportunity of implementing reconfigurable geometric pathways in free-space optical interconnect architectures. Reconfigurable geometric pathways would allow for the post-packaging alignment of optical interconnects and the implementation of optical interconnect based recovery schemes for VLSI. In addition, bulk devices would have application in space based optical communication systems.
Optical scanners have been implemented using electro-mechanical, acousto-optic, and electro-optic schemes. Most previous electro-optic implementations of optical scanners have essentially relied upon affecting a variable prism shaped index variation utilizing triangular electrode patterns in bulk material. One reported optical scanner implemented in lithium tantalite relied upon a phased array scheme. The physical structure of the bulk phased array scanner resulted in substantial grating lobe formation which limited the achievable scan angle. The previous prism and phased array schemes all required substantial electro-optic interaction length in order to affect scanning. This requirement is incompatible with the implementation of integrated devices.
Quadratic lead lanthanum zirconate titanate (PLZT) compositions permit the implementation of novel and integrated structures that affect optical scanning and reconfigurable optical array generation based upon phased array schemes. The electro-optic interaction lengths of the phased array based structures allow for integration with VLSI electronics. These PLZT phased array based structures can facilitate the practical implementation of reconfigurable geometric pathways in optical interconnect architectures.
The task of improving phased array optical scanners is alleviated, to some extent, by the systems described in the following U.S. patents, the disclosures of which are incorporated herein by reference:
U.S. Pat. No. 4,115,747 issued to Sato et al; PA0 U.S. Pat. No. 4,243,300 issued to Richards et al; PA0 U.S. Pat. No. 4,636,786 issued to Haertling; PA0 U.S. Pat. No. 4,854,669 issued to Birnbach et al; PA0 U.S. Pat. No. 5,115,344 issued to Jackie; and PA0 U.S. Pat. No. 5,159,456 issued to Takanashi et al;
U.S. Pat. No. 4,115,747 issued to Sato et al is directed to an optical modulator using a controllable diffraction grating. The Sato diffraction grating, corresponding to the Journal of Applied Physics article cited in the disclosure statement, utilizes interdigital electrodes formed on a substrate comprised of an electro-optic material such as lead lanthanum zirconium titanate (PLZT). The preferred embodiment of the Sato diffraction grating, however, includes an opaque substrate formed of lead-zirconate-titanate (PZT) which cannot be used in accordance with this invention because the Sato diffraction grating operates in reflective mode only. In addition, the interdigital electrodes disclosed in the Sato patent are limited to being formed from metals, such as gold, silver and aluminum.
U.S. Pat. No. 4,854,669 issued to Birnbach et al discloses a spatial filter containing a layer of electro-optic material with electrodes placed thereon to form a number of individual addressable concentric annular bands of different radii. Each of the individual bands can be supplied with a variable voltage so as to change the transmissivity of each band or, more generally, the entire transmissivity of the opto-electric layer in continuous fashion from highly transparent to highly opaque. The Birnbach filter is used in conjunction with an optical image processor that modulates and processes real time X-ray images by suppressing or filtering undesired spatial frequencies while passing a desired range or ranges of spatial frequencies. The spatial filter comprises two conductive layers made of indium tin oxide (ITO), an opto-electric layer formed of a single crystal PLZT, and a silver reflective layer backed with three to four microns of copper to prevent oxidation. A modification of the disclosed optical image processor includes a diffraction grating used in combination with a cluster of Birnbach spatial filters stacked three deep at second order points, two deep at first order points, and singularly placed at zero order points to achieve balance processing of the image data provided at the various order points by the diffraction grating.
The Takanashi et al patent, U.S. Pat. No. 5,159,456, is directed to a photo-to-photo transducer. The transducer is a laminated device including a photo conductive layer composed of amorphous silicon which has formed thereon transparent ITO electrodes. The laminated transducer also includes a photo modulation layer composed of either a liquid crystal layer of the scattering type and PLZT or the composite membrane of a macro-molecule and liquid crystal. These two alternative compositions are used instead of the prior art photo modulation layer composed of a monocrystal of lithium niobate whose refractive index varies with electric field due to the electro-optic effect. The Takanashi patent is specifically directed to utilizing a PLZT layer having transparent ITO electrodes in place of the prior photo modulating layer.
U.S. Pat. No. 4,636,786 issued to Haertling discloses an improved electro-optic ceramic display which incorporates transparent interdigital ITO electrodes being disposed on a PLZT substrate. The electrodes are supplied voltage to produce the electro-optic birefringent effect, i.e., a change in the substrates index of refraction as a function of voltage applied to the interdigital electrodes. Haertling utilizes the known relationship that for certain compositions comprising PLTZ materials, the differences in velocities, or indexes of refraction, caused by a change in applied voltage to the ITO electrodes results in a quadratic ceramic material.
Cited herein as relevant background art, U.S. Pat. No. 5,115,344 to Jackie is directed to a tunable diffraction grating composed of rows of an electrically conductive material deposited on a deformable which is transparent to light of numerous wavelengths. The rows of electrically conductive material are connected to a source of voltage which, when applied, causes the electrode rows to be either repelled or attracted relative to each other, thus increasing or decreasing the spacing of the rows and allowing different wavelengths of light to be diffracted.
Finally, U.S. Pat. No. 4,243,300 issued to Richards et al and cited herein as general background art, discloses an electro-optical modulator/antenna which operates in the tunable diffraction grating mode to vary the magnitude of zero diffraction order. The Richards modulator is composed of a thin substrate of lithium niobate which includes at least one set of metallic interdigital electrodes deposited on the lateral surface or Just below the lateral surface of the substrate. The Richards patent employs the known result that a variable electric field between adjacent electrodes changes the crystal's index of refraction in accordance with the linear transverse Pockel's effect. The Richards patent teaches that a cooperation between the diffraction grating phenomenon and the Pockel's effect can be employed to eliminate the possibility of arcing between adjacent electrodes as the zero diffraction order is modulated.